The invention is directed to a method for joining thin plates stacked on one another by stamping pressing and swaging dies and to an apparatus for performing the method.
Connecting metal sheets by means of stamping dies has already been known for a long time (German Patent No. 8 73 237). The main problem in this joining technique is in processing the material precisely, with a corresponding ability to replicate the joining quality. This technique is particularly complicated because of the fact that in it, a deep-drawing and stamping operation is combined with an ensuing upsetting or swaging operation, and while the relative tool movement between the upper die and the bottom die is effected coaxially, the movement of the material takes place first in this same axis but later, in the course of the swaging operation, radially thereto. Controlling this radial movement in terms of replicability is particularly difficult.
In a known method and apparatus for performing this joining method of the type defining the prior art (German Patent No. 23 38 460), after the stamping and pressing operation the bottom die is retracted relative to the counterpressure face, which in this case is provided on a flattening die, far enough that only one of the two pieces of plate is located inside the bottom die, so that only the other piece of plate can be enlarged during the swaging operation. This method has the disadvantage that the plates that are fixed in place for being worked on are loosened when the bottom die is retracted, and this retraction gives rise to the danger that the plates will not be joined together in a form-fitting manner. A further substantial disadvantage is that the apparatus has to be relatively complicated in structure, in order to perform this retraction of the bottom die while simultaneously retaining the flattening die in position. Still another disadvantage resides in that a further operation is required in order to eject the workpiece from the bottom die.